The present invention relates to a resistor for use in hybrid ICs and various other electronic devices. The present invention also relates to a process for producing the resistor and a thermal head using the resistor. In particular, the present invention relates to a thin uniform resistor that contains iridium (Ir) and which can be produced by a thick-film process, and also relates to a process for producing the resistor, as well as to a thermal head using it.
There have been two basic approaches for fabricating resistors useful in electronic devices such as hybrid ICs and thermal heads; one is a thick-film process in which a coating of thick-film resistive paste is formed on a substrate which is then fired to make a resistor, and the other method is a thin-film process employing sputtering or other thin-film depositing techniques.
In a thick-film process, a powder mixture of ruthenium oxide and glass frit is dispersed in an organic vehicle made of a solvent and a resin and the resulting thick-film resistive paste is screen-printed on a substrate, which is then fired to make a resistor.
In a thin-film process which employs vacuum technology, a thin film of a refractory metal such as tantalum is deposited on a substrate by sputtering and a patterned thin-film resistor is fabricated by photolithographic techniques. This method is used to fabricate some of the thermal heads in current use.
The conventional thick-film process which uses thick-film resistive paste have the advantage of achieving high production rate with inexpensive facilities. However, on account of their large thickness (.gtoreq.10 .mu.m) and because of the inhomogeneity of the thick-film paste which is made of glass frit and ruthenium oxide powder, the resistors produced by this process have the problem of low strength to an electric field, i.e. their resistance changes sharply when they are subjected to voltage variations.
Further, the thick-film process has additional disadvantages; the value of resistance of the final product cannot be effectively controlled by adjusting the proportions of glass frit and ruthenium oxide alone and great variations in resistance will occur not only because of the difference in the particle sizes of glass frit and ruthenium oxide powder but also depending upon the firing temperature used. Even if the same compositional range and average particle size are used, the value of resistance will differ from one lot to another.
The thin-film process is capable of producing uniformly thin film resistors but, on the other hand, this method requires expensive facilities and achieves only a low production rate.